There exists a significant problem with potential collisions between aircraft (or ground vehicles) and other aircraft (or ground vehicles) during operations on the surface of the airport, particularly at night or in low-visibility conditions.
Current collision-avoidance systems, such as traffic collision avoidance systems (TCAS) are effective only when aircraft are airborne. Also, relatively few large airports are equipped with radar that can monitor surface traffic, and even where it is available this radar usually has many “blind spots” on the airport where detection of airplanes or vehicles is not possible.